Mass of lymphatic tissue giving don ideas (8)
I believe the answer is:
adenoids
'mass of lymphatic tissue' is the definition.
'adenoids' can be an answer for 'tissue' (I've seen this before). I am not certain of the 'mass of lymphatic' bit.
'giving don ideas' is the wordplay.
'giving' indicates anagramming the letters (the letters give the letters for another word).
'don'+'ideas'='donideas'
'donideas' is an anagram of 'ADENOIDS'.
Can you help me to learn more?
(Other definitions for adenoids that I've seen before include "Glandular tissue at back of nose" , "They affect the voice" , "Enlarged spongy tissue between back of nose and throat" , "Enlarged spongy tissues between back of nose and throat" , "Lymph tissue towards back of throat" .)